1. Field of the Invention
This invention relates to the field of data recording schemes for magnetic media storage systems.
2. Background Art
Mass storage for computer systems is typically provided by magnetic media storage systems, such as rigid or flexible disk storage systems. A rotating disk having a magnetic media layer on the surface is accessed by a "read/write" head which is used to store and retrieve information from the disk's surface. To store information on a magnetic media disk, flux reversals are induced in the magnetic particles comprising the disk's surface. When a magnetic read/write head is passed over the flux reversals, a signal is induced in the head which is sinusoidal in nature. In the prior art, detection of this information signal is typically amplitude-based. That is, the amplitude of the signal is used to indicate the present or absence of magnetic flux reversals. Reversals are then interpreted as "ones" or "zeros" according to the coding algorithm.
To maximize disk performance and storage capability, it is desired to increase the data density on the surface of the disk. This is accomplished by increasing the frequency of the flux transitions used to encode the digital data. However, as the data frequency increases, that is, as the flux reversals are moved closer to each other on the disk's surface, they interfere with each other, lowering the amplitude. The read/write head detects changes in the magnetic field on either side of a small gap in the head. If two written transitions are the same distance apart as the gap is long, the head can't note the flux change and detects no transition. This gap null area forms the upper limit of peak detection coding schemes. One prior art attempt to break this barrier uses zero crossing of the signal generated by the flux transition to indicate digital information. For example, in Heidecker, U.S. Pat. No. 3,603,942, a zero crossing data detection scheme is implemented. In Heidecker, two write frequencies are implemented. The first write frequency is used to create a zero crossing representing a zero (or "one"). A second write frequency, approximately twice that of the first, is used to create flux transitions so close together that no zero crossing results. This absence of a zero crossing represents a logical "one" (or zero). One disadvantage of the method of Heidecker is its reliance on pre-compensation of the information signal. Precompensation lowers the amplitude of the information signal and can introduce offset into the actual zero crossing location. In addition, inter-symbol interference (ISI) causes signal spread and reduces the slope at the zero crossing location. Finally, the pre-compensation scheme of Heidecker is pattern dependent. It would be desirable to provide a method for high-density data recording which is pattern independent.
Therefore, it is an object of the present invention to provide a high-density data recording and detection scheme which is pattern independent.
It is another object of the present invention to provide a high-density data recording and detection scheme which is less sensitive to the effects of inter-symbol interference.
It is yet another object of the present invention to provide a high-density data recording and detection scheme which does not rely on pre-compensation of the information signal.
It is still another object of the present invention to provide a high-density data recording and detection scheme which is self compensating for pattern induced AC and DC wave form shifts.
It is a still further object of the present invention to provide a high-density data recording and detection scheme which is less sensitive to AC and DC signal variations such as those induced by buried servo patterns.